Composite plating or codepositing plating is to codeposit water-insoluble materials such as inorganic or organic particles or fibers in a metal deposit to form a composite film in which the particles or fibers are dispersed in the metal matrix. For uniformly codepositing the particles or fibers in the plating film, it is important to keep the particles or fibers uniformly dispersed in the plating solution.
A plating apparatus of the pump agitation type is known in the prior art for effectively conducting composite plating. A pump is connected to a conduit which is extended along the bottom of a plating tank. Plating solution is circulated by a pump through the conduit to form solution streams to thereby agitate the plating solution so that the particles or fibers may be uniformly dispersed in the plating solution.
This plating apparatus is based on an agitation mechanism using a pump located outside the tank which draws the plating solution in the tank and returns it to the tank by injecting it at the tank bottom. With this mechanism, pump suction tends to induce turbulent and vortex flows in the tank solution, sometimes interfering with the uniform dispersion of particles or fibers in the plating solution.
A modified version of composite plating apparatus for preventing occurrence of turbulent and vortex flows in the plating solution due to pump suction is illustrated in FIG. 5 as comprising a plating tank (a) and a reservoir (b) disposed adjacent the plating tank. A circulating pump (d) is disposed outside the tank and reservoir and has connected thereto a suction conduit (e) and a discharge conduit (h) followed by a spray conduit (g) having a plurality of orifices (g). The pump (d) is effective for returning the plating solution (c) from the reservoir (b) to the plating tank (a) through the conduits. This composite plating apparatus of the overflow type, however, is relatively large in size because it requires space for installing the pump and piping.